Modulus Ratio and Joint Factor Concepts to Predict Rock Mass Response

The commonly adopted rock mass classifications, namely RMR, Q and GSI, are used to estimate compressive strength and modulus of rock masses. These values have been examined as per modulus ratio concept, M _rj , for their reliability. The design parameters adopted in some of the recent case studies based on these classifications indicate that the M _rj values for rock masses are higher than those of the corresponding intact rocks. The joint factor, J _f, which is defined as a weakness coefficient in rock mass suggests that modulus ratio of rock mass (M _rj ) has to be less than the modulus ratio of the corresponding intact rock (M _ri ), on the basis of extensive experimental evidence. With joint factor, compressive strength, elastic modulus, cohesion and friction angle were estimated and applied in the analyses of a few cases. The predictions of deformations with this approach agreed well with the field measurements by adapting equivalent continuum approach. The modulus ratio concept is considered to present a unified classification for intact rocks and rock masses. Soil–rock boundary, standup time in under ground excavations and also penetration rate of TBM estimates have been linked to M _rj .